Electrical contacts in layered structures

ABSTRACT

Provided herein are layered structures and methods for forming the same, the layered structures including a conductive layer and an overcoat layer formed on a surface thereof, one or more electrical contacts formed on the surface of the conductive layers and via openings extending through the overcoat layer and reaching the electrical contacts.

CROSS-REFERENCES TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 62/022,502, filed Jul. 9, 2014, whichapplication is incorporated herein by reference in its entirety.

BACKGROUND

Conductive nanostructures have been used to form thin conductive films,referred to as a nanostructure layer. In the nanostructure layer, one ormore electrically conductive paths are established through continuousphysical contacts among the conductive nanostructures. Generallydescribed, the nanostructure layer may be formed by depositing a liquiddispersion (or coating composition) comprising a liquid carrier and aplurality of the conductive nanostructures. Upon the liquid dispersiondrying, a nanostructure layer of networking nanostructures is formed.The nanostructure layers are suitably transparent for a variety of usesin flat panel electrochromic displays, with one such use being as atransparent electrode.

BRIEF SUMMARY

One embodiment provides a method of forming a layered structure, themethod comprising: providing a conductive layer on a substrate, theconductive layer having a surface opposite from the substrate; formingone or more electrical contacts on the surface of the conductive layer;forming an overcoat layer over the one or more electrical contacts, theovercoat layer contacting the surface of the conductive layer uncoveredby the electrical contacts; and providing one or more via holes in theovercoat layer, the one or more via holes extending through the overcoatlayer and reaching at least some of the one or more electrical contacts.

In a further embodiment, forming the overcoat layer comprises depositingand curing an overcoat material. In various embodiments, the overcoatmaterial may be a reflowable polymer. For instances, the reflowablepolymer includes at least one material selected from the groupconsisting of poly(methyl methacrylate), a dissolved powder coatingresin, a copolymer of methyl methacrylate, a hydroxyl functionalmonomer, a carboxylate functional monomer, an amine monomer, and anepoxy monomer.

In another embodiment, forming the one or more via holes comprises laserablating the overcoat layer at predetermined locations.

In yet another embodiment, forming the one or more via holes comprisesdewetting the overcoat material at the one or more electrical contacts.

In further embodiments, forming the overcoat layer comprising overlayinga functional film on the surface of the conductive layer, and formingthe one or more via holes comprises pre-cutting the functional film atpredetermined locations prior to overlaying the functional film on thesurface of the conductive layer.

In various embodiments, forming the one or more electrical contactscomprises spot-depositing a formulation having conductive nanoparticleson the surface of the conductive layer.

In other embodiment, forming one or more electrical conduits through theone or more via holes, wherein the one or more electrical conduitscontact the one or more electrical contacts. For instances, the one ormore electrical conduits may be conductive wires, conductive adhesive orsolder.

In various embodiments the conductive layer comprises a plurality ofnetworking conductive nanostructures, including silver nanowires, carbonnanotubes, or a combination thereof.

A further embodiment provides a layered structure comprising: asubstrate; a conductive layer formed on the substrate, the conductivelayer including a plurality of networking conductive nanostructures,wherein the conductive layer has a surface opposite from the substrate;one or more electrical contacts on the surface of the conductive layer;an overcoat layer overlying the conductive layer, wherein the overcoatlayer contacts the surface uncovered by the one or more electricalcontacts; and one or more via holes extending through the overcoat layerand reaching the one or more electrical contacts.

In various embodiments, the conductive nanostructures include silvernanowires, carbon nanotubes or a combination thereof.

In other embodiments, each electrical contact includes a plurality ofconductive particles.

In further embodiments, the overcoat layer is a reflowable polymer or afunctional film.

In yet further embodiments, the layered structure further comprises oneor more electrical conduits extending into the one or more via holes andcontacting the one or more electrical contacts.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elements.The sizes and relative positions of elements in the drawings are notnecessarily drawn to scale. For example, the shapes of various elementsand angles are not drawn to scale, and some of these elements arearbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn are not intendedto convey any information regarding the actual shape of the particularelements, and they have been solely selected for ease of recognition inthe drawings.

FIG. 1 is a cross-section view of a portion of one embodiment of alayered structure in accordance with aspects of the present disclosure.

FIGS. 2A-2C are cross-section views of a portion of structures inaccordance with aspects of the present disclosure.

FIGS. 3A-3D illustrate an embodiment for forming a conductive contactusing a buried contact in accordance with aspects of the presentdisclosure.

FIG. 4 is a cross-section view of a portion of another embodiment of astructure in accordance with aspects of the present disclosure.

FIG. 5 is a top view of a portion of another embodiment of a structurein accordance with aspects of the present disclosure.

FIG. 6A is a side view of a structure having voids in the coating layerin accordance with aspects of the present disclosure.

FIG. 6B is a side view of the structure in FIG. 6A illustrating thevoids filled with conductive plugs.

FIG. 7 is a system for forming a structure in accordance with aspects ofthe present disclosure.

FIG. 8 is a display incorporating a layered structure in accordance withaspects of the present disclosure.

FIG. 9 is a touch screen device incorporating a layered structure inaccordance with aspects of the present disclosure.

FIG. 10 is a top view of a structure illustrating an exemplary contactpad layout in accordance with aspects of the present disclosure.

FIGS. 11A-11D illustrate an example used to form a structure inaccordance with aspects of the present disclosure.

FIGS. 12A-12D illustrate an example used to form a structure inaccordance with aspects of the present disclosure.

FIGS. 13A-13E illustrate an structure and method of forming a contactthrough an overcoat in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

As indicated above, the nanostructure layers described herein aresuitably transparent and electrically conductive for a variety of usesin flat panel electrochromic displays. Typically, such displays includea conductive shielding layer to protect against electromagneticinterference (EMI) and electrostatic discharge (ESD). In variousembodiments, the nanostructure layers described herein provide aconductive and transparent shielding layer, which may, in oneembodiment, be used for providing EMI and ESD shielding for/between thetouch sensor, display, or their combination. In other embodiments, thenanostructure layers described herein may also comprise a driving orsensing layer for a capacitive touch sensor; an electrode for chargeinjection into or withdrawal from an OLED lighting device orphotovoltaic cell; an electrode for driving a display device such as aliquid crystal, OLED, or electronic paper display; and the like.

Various embodiments of the present disclosure are directed to layeredstructures that include a nanostructure layer with coating layer formedon a surface thereof. The coating layer may be applied to thenanostructure layer as a liquid coating solution and dried or hardenedto form a solid coating layer; the coating layer may also consist of apre-formed solid film which is laminated or otherwise adhered to thenanostructure layer. The nanostructure layer is configured to be placedin electrical communication with another component, such as ground or anelectrical circuit. In various embodiments, the coating layer includesone or more conductive contacts that are configured to electricallycouple the nanostructure layer to the outer surface of the coatinglayer. In some embodiments, the structure further includes a substrateand is used as a shielding layer in flat panel electrochromic displays,such as liquid crystal displays (LCD), touch panels, and the like. Thecoating layer may be configured to provide mechanical and/or chemicalprotection to one or both of the substrate and the nanostructure layer.The coating layer may also be used to for enhanced appearance, such asto reduce glare, reflection, or any other purpose. In that regard, thecoating layer may have an anti-glare film or anti-reflecting film formedon a surface thereof or formed in a surface thereof.

FIG. 1 shows a layered structure 100 in accordance with one embodimentof the present disclosure. The structure 100 may be at transparent orhave portions that are transparent. The structure 100 comprises coatinglayer 102 having opposite outer and inner surfaces 104, 106. The innersurface 106 of the coating layer 102 is on a first surface 108 of ananostructure layer 110. A second surface 112 of the nanostructure layer110 is on a first surface 114 of a substrate 116. In one embodiment, thecoating layer 102 is formed on the first surface 108 of thenanostructure layer 110 thereby adhering the coating layer to thenanostructure layer 110. In another embodiment, a portion of thenanostructure layer 110 is formed on the first surface 114 of thesubstrate 116, thereby adhering the nanostructure layer 110 to thesubstrate 116. In yet another embodiment, the nanostructure layer 110 isformed on the inner surface 106 of the coating layer 102 and thesubstrate 116 is adhered to the nanostructure layer 110.

In various embodiments, the layered structures described herein provideone or more surface contacts proximate the outer surface of the coatinglayer 102 at predetermined locations or randomly distributed. Thesurface contacts may be provided over a particular area or over theentire area of the coating layer. The stacks can be customized by theend user into any configuration (size, shape, and the like) whilemaintaining sufficient surface contacts. Certain embodiments providecontact through a thick coating layer or barrier layer (e.g. thickerthan 0.2 μm, thicker than 1 μm or even thicker than 3 μm).

In some embodiments, the structure 100 is formed from a larger sheetcomprising the protective coating layer, the nanostructure layer, andthe substrate and then subsequently cut into individual structures of aparticular size and shape to form the structure 100.

FIGS. 2A-2C illustrate other structures 200A-200C in accordance withaspects of the present invention. The structures 200A-200C are similarin structure to the structure 100 in FIG. 1, except that the structures200A-200C include one or more conductive contacts 202 along a sidesurface of at least a portion thereof. In the embodiments shown in FIGS.2A-2C, a conductive contact 202 is in electrical communication with thenanostructure layer 110 via a side surface of the nanostructure layer110. In particular, the conductive contact 202 may be in electricalcontact with one or more conductive nanostructures formed in theconductive layer 110.

As shown in FIG. 2A, the conductive contact 202 may be locatedperpendicular with the side surface of the structure 200A and extendfrom the outer surface 104 of the coating layer 102 to a second surface118 of the substrate 116. As shown in FIG. 2B, the conductive contact202 may be at an angle relative to the structure 200B and in some cases,extend beyond the outer surface 104 of the coating layer 102. As shownin FIG. 2C, the conductive contact 202 may be located on the firstsurface 108 of the nanostructure layer 110 extending along a sidesurface of the coating layer 102 and remain below the outer surface 104of the coating layer 102. Although the conductive contact shown in FIG.2A is flush with the outer surface 104 of the coating layer, theconductive contact in FIG. 2B extends beyond the outer surface 104 ofthe coating layer 102, and the conductive contact 202 in FIG. 2C isbelow the outer surface of the coating layer, it is to be appreciatedthat each embodiment may extend above, be flush with, or remain belowthe outer surface 104 of the coating layer 102. It is to be appreciatedthat the side surface of the structures may include imperfections due tothe cutting process that may advantageously expose nanostructures,thereby encouraging electrical contact between the nanostructure layer110 and the conductive contact 202.

In one embodiment, the conductive contact 202 comprises liquidconductive paste, paint, or conductive epoxy, such as those comprisingsilver, copper, nickel, aluminum, graphite, carbon, and the like, andany combination thereof. In another embodiment the conductive contact202 comprises a conducting tape, such as copper or aluminum tape. Inanother embodiment, the conductive contact 202 comprises a conductinglayer deposited by a vapor deposition or an electrochemichal depositionprocess, such as evaporation, sputtering, chemical vapor deposition,electroplating, or electroless plating.

In another embodiment, at least one buried contact may be formed in thestructure, such as on the first surface 108 of the nanostructure layer110, before the coating layer 102 is formed thereon. FIGS. 3A-3Dillustrate one embodiment for forming a conductive contact using aburied contact. As shown in FIG. 3A, a buried contact 203, such asconductive ink or conductive film, may be formed on the first surface108 of the nanostructure layer 110. In one embodiment, the buriedcontact 203 is located proximate the perimeter of each individualstructure on a sheet. In particular, the buried contact may be placedalong a cutting line (the dotted line shown in FIG. 3C), such that whenthe sheet is cut into the individual structures, the conductive ink orfilm is exposed at the side or cut surface thereof. As shown in FIG. 3B,the coating layer 102 is formed on or attached to the first surface 108of the nanostructure layer 110 and the buried contact 203. As shown inFIG. 3C, the structure is cut thereby exposing a portion of the buriedcontact 203. As shown in FIG. 3D, a conductive contact 202 is formed onthe side surface of the structure.

In some embodiments, the buried contacts 203 or conductive contacts 202are placed at one or more particular locations at the perimeter of theindividual structures. In such embodiments, the center portion of thestructures may remain transparent, while the buried contacts may reducethe transparency at the perimeters. In some embodiments, the buriedcontacts are between approximately 1 μm and approximately 5 μm thick.

As shown in the illustrated embodiment, the side surface of thenanostructure layer 110 may be further coupled to another electricalcircuit or ground, thereby configuring the structure 100 to protect adisplay or touch panel incorporating the structure 100 therein fromelectrical side effects, such as ESD and EMI, or to providefunctionality such as capacitive touch sensing.

FIG. 4, there is shown a structure 400 in accordance with anotherembodiment of the present disclosure. The structure 400 is similar tothe structure 100 in FIG. 1, except that the structure 400 may includeone or more conductive plugs 204 within the coating layer 102. The plugs204 comprise a conductive material and are configured to span from theouter surface 104 of the coating layer 102 to the inner surface 106 ofthe coating layer 102, thereby forming an electrical path through thecoating layer 102.

An inner surface of the conductive plugs 204 is proximate the innersurface 106 of the coating layer 102 and is in electrical contact withthe first surface 108 of the nanostructure layer 110 or with aconductive material there between, such as bonding material. In thatregard, the inner surface of the conductive plugs 204 is in electricalcommunication with the conductive nanostructures in the nanostructurelayer 110. An outer surface of the conductive plugs 204 is exposed atthe outer surface 104 of the coating layer 102. In the illustratedembodiment, the outer surface of the conductive plugs 204 extends abovethe outer surface 104 of the coating layer 102. In that regard, theconductive plugs 204 may have at least one dimension, such as a lengthor a diameter, which is greater than the thickness of the coating layer102. It is to be appreciated, however, that the conductive plugs 204 maybe equal to or less than the thickness of the coating layer 102 so longas a portion of the conductive plugs 204 is exposed from the coatinglayer 102 (i.e. not covered by the coating layer). The plugs 204 maycomprise a single conductive particle or a plurality of conductingparticles, and may also comprise a combination of conducting andnon-conducting materials, so long as a conducting path is establishedthrough the plug.

The exposed portion of the outer surface of the conductive plugs 204provides conductive surface contacts. In that regard, a portion of theouter surface 104 of the coating layer 102 may be placed in electricalcommunication with the nanostructure layer 110. As is shown in theillustrated embodiment, the exposed portion that provides conductivesurface contacts may be coupled to ground or to an electrical circuit420. It is to be appreciated that when the outer surface of theconductive plugs 204 is in electrical communication with ground, thestructure 300 may provide a useful function, such as EMI or ESDshielding for the display or touch panel.

Conductive Nanostructures

Generally described, the conductive nanostructures (or nanowires)referred to above are nano-sized conductive structures that are used toform thin conductive films. In the thin conductive films, one or moreelectrically conductive paths are established through continuousphysical contacts among the nanostructures. A conductive network ofnanostructures is formed when sufficient nanostructures are present toreach an electrical percolation threshold. The electrical percolationthreshold is therefore an important value above which long rangeconnectivity can be achieved. In general, the conductive nanostructurehave at least one dimension of which is less than 500 nm, morepreferably, less than 250 nm, 100 nm, 50 nm or 25 nm.

The nanostructures can be of any shape or geometry. In certainembodiments, the nanostructures are isotropically shaped (i.e., aspectratio=1). Typical isotropic nanostructures are nanoparticles, which maybe the same or different from the nanoparticles that form plugs. Inpreferred embodiments, the nanostructures are anisotropically shaped(i.e., aspect ratio≠1). As used herein, “aspect ratio” refers to theratio between the length and the width (or diameter) of thenanostructure. The anisotropic nanostructure typically has alongitudinal axis along its length. Exemplary anisotropic nanostructuresinclude nanowires and nanotubes, as defined herein.

The nanostructures can be solid or hollow. Solid nanostructures include,for example, nanoplugs and nanowires. “Nanowires” thus refers to solidanisotropic nanostructures. Typically, each nanowire has an aspect ratio(length:diameter) of greater than 10, preferably greater than 50, andmore preferably greater than 100. Typically, the nanowires are more than500 nm, more than 1 μm, or more than 10 μm long.

Hollow nanostructures include, for example, nanotubes. Typically, thenanotube has an aspect ratio (length:diameter) of greater than 10,preferably greater than 50, and more preferably greater than 100.Typically, the nanotubes are more than 500 nm, more than 1 μm, or morethan 10 μm in length.

The nanostructures can be formed of any electrically conductivematerial. Most typically, the conductive material is metallic. Themetallic material can be an elemental metal (e.g., transition metals) ora metal compound (e.g., metal oxide). The metallic material can also bea bimetallic material or a metal alloy, which comprises two or moretypes of metal. Suitable metals include, but are not limited to, silver,gold, copper, nickel, gold-plated silver, platinum and palladium. Theconductive material can also be non-metallic, such as carbon or graphite(an allotrope of carbon).

Nanostructure Layer

As indicated above, a nanostructure layer has been used as a transparentelectrode in displays. As described herein, however, nanostructurelayers can also be used as a shielding layer to protect againstelectrical EMI and ESD. The nanostructure layer (also referred to as atransparent conductor layer) is formed by depositing a liquid dispersion(or coating composition) comprising a liquid carrier and a plurality ofconductive nanostructures, and allowing the liquid carrier to dry.

The nanostructure layer comprises nanostructures, such as thosedescribed above, that are randomly distributed and interconnect with oneanother. As the number of the nanostructures reaches the percolationthreshold, the thin film is electrically conductive. Other non-volatilecomponents of the ink composition, including, for example, one or morebinders, surfactants and viscosity modifiers, may form part of theconductive film. Thus, unless specified otherwise, as used herein,“conductive film” and “nanostructure layer” and “nanowire layer” referto, interchangeably, a nanostructure layer formed of networking andpercolative nanostructures combined with any of the non-volatilecomponents of the ink composition, and may include, for example, one ormore of the following: viscosity modifier or a binder, surfactant andcorrosion inhibitor.

The liquid carrier for the dispersion may be water, an alcohol, a ketoneor a combination thereof. Exemplary alcohols may include isopropanol(IPA), ethanol, diacetone alcohol (DAA) or a combination of IPA and DAA.Exemplary ketones may include methyl ethyl ketone (MEK) and methylpropyl ketone (MPK).

The surfactants serve to reduce aggregation of the nanostructures and/orthe light-scattering material. Representative examples of suitablesurfactants include fluorosurfactants such as ZONYL® surfactants,including ZONYL® FSN, ZONYL® FSO, ZONYL® FSA, ZONYL® FSH (DuPontChemicals, Wilmington, Del.), and NOVEC™ (3M, St. Paul, Minn.). Otherexemplary surfactants include non-ionic surfactants based on alkylphenolethoxylates. Preferred surfactants include, for example, octylphenolethoxylates such as TRITON™ (×100, ×114, ×45), and nonylphenolethoxylates such as TERGITOL™ (Dow Chemical Company, Midland Mich.).Further exemplary non-ionic surfactants include acetylenic-basedsurfactants such as DYNOL® (604, 607) (Air Products and Chemicals, Inc.,Allentown, Pa.) and n-dodecyl β-D-maltoside.

The viscosity modifier serves as a binder that immobilizes thenanostructures on a substrate. Examples of suitable viscosity modifiersinclude hydroxypropyl methylcellulose (HPMC), methyl cellulose, xanthangum, polyvinyl alcohol, carboxy methyl cellulose, and hydroxy ethylcellulose.

In particular embodiments, the weight ratio of the surfactant to theviscosity modifier in the coating solution is preferably in the range ofabout 80:1 to about 0.01:1; the weight ratio of the viscosity modifierto the conductive nanostructures is preferably in the range of about 5:1to about 0.000625:1; and the weight ratio of the conductivenanostructures to the surfactant is preferably in the range of about560:1 to about 5:1. The ratios of components of the coating solution maybe modified depending on the substrate and the method of applicationused. A preferred viscosity range for the coating solution is betweenabout 1 and 100 cP.

In one embodiment, the coating solution may initially contain a binder(e.g., HPMC) to facilitate film forming. In some embodiments, the binderis removed thereafter such that the nanostructures form a discontinuouslayer and do not interfere with the optical interaction between theanti-reflective layer and the organic stack.

The electrical conductivity of the conductive film is often measured by“sheet resistance,” which is represented by Ohms/square (or “ohms/sq”).The sheet resistance is a function of at least the surface loadingdensity, the size/shapes of the nanostructures, and the intrinsicelectrical property of the nanostructure constituents. As used herein, athin film is considered conductive if it has a sheet resistance of nohigher than 10⁸ ohms/sq. Preferably, the sheet resistance is no higherthan 10⁴ ohms/sq, 3,000 ohms/sq, 1,000 ohms/sq or 350 ohms/sq, or 100ohms/sq. Typically, the sheet resistance of a conductive network formedby metal nanostructures is in the ranges of from 10 ohms/sq to 1000ohms/sq, from 100 ohms/sq to 750 ohms/sq, 50 ohms/sq to 300 ohms/sq,from 100 ohms/sq to 500 ohms/sq, or from 100 ohms/sq to 250 ohms/sq, or10 ohms/sq to 300 ohms/sq, from 10 ohms/sq to 50 ohms/sq, or from 1ohms/sq to 10 ohms/sq. For the opto-electrical devices described herein,the sheet resistance is typically less than 20 ohms/square, or less than15 ohms/square, or less than 10 ohms/square.

Optically, the nanostructure-based transparent conductors have highlight transmission in the visible region (400 nm-700 nm). Typically, thetransparent conductor is considered optically clear when the lighttransmission is more than 70%, or more typically more than 85% in thevisible region. More preferably, the light transmission is more than90%, more than 93%, or more than 95%. As used herein, unless specifiedotherwise, a conductive film is optically transparent (e.g., more than70% in transmission). Thus, transparent conductor, transparentconductive film, layer or coating, conductive film, layer or coating,and transparent electrode are used interchangeably.

In general, the thickness of the nanostructure layer is between 10 nmand 1000 nm and in some embodiments, between 20 nm and 200 nm. In yetsome embodiments, the thickness is between 70 nm and 130 nm, and in oneembodiment, the thickness of the nanostructure layer is 100 nm.

Coating Layer

In various embodiments, the coating layer comprises an insulativematerial and may have one or more portions that are substantiallytransparent, such as between about 440 nm to 700 nm. Non-limitingexamples include resins, polymers, and the like. The coating layer maybe a UV-cured resin such as an acrylic, urethane acrylate, or epoxyacrylate. Or it may be a thermally cured resin, such as an epoxy orsilicone. Or it may be a thermoplastic resin, i.e. a non-crosslinkedhigh molecular weight polymer which is solid under storage and operatingconditions, but can be melted by heating or dissolved in a solvent. Insome embodiments, conductive material is formed in the coating layer.

The coating layer may be formed from a flowable material, such as anovercoat, and in some embodiments may require one or more curing orbaking step to harden the material. The coating layer may be formed onthe nanostructure layer such that the coating layer cures or dries onthe nanostructure layer. In other embodiments, the coating layer is apre-existing film that is bonded to the nanostructure layer, e.g. by alamination process.

In some embodiments, one or more layers of the coating layer functionsas an anti-glare and/or anti-reflective coating. Curing as referred toherein may include any curing process that causes the coating layer toform a solid material, such as by cross-linking. Nonlimiting examplesinclude irradiating the coating layer material with visible orultraviolet (UV) light, electron beams, thermal curing, and the like.

In general, the coating layer may mechanically and/or chemically protectthe substrate and/or the nanostructure layer, such as protect thenanostructure layer from environmental factors that can damage thenanostructure layer. In that regard, one or more layers of the coatinglayer may have a hardness rating that is greater than the hardnessrating of the nanostructure layer. In some embodiments, the coatinglayer may have a pencil hardness rating of between 2H-5H, with oneembodiment being 3H. The coating layer can also act as a chemicalbarrier, reducing the rate at which liquids, gases, and substancesdissolved or suspended therein can come in contact with thenanostructure layer from the environment.

It is to be appreciated that the coating layer may be formed of one ormore layers. Each layer may be formed of a different material, have adifferent thickness, and formed by a different process than the otherlayers of the coating layer.

Substrate

The substrate may comprise one or more insulative and/or conductivematerials and in some embodiments may have one or more portions that aresubstantially transparent, such as between about 440 nm to 700 nm. Thesubstrate may be rigid, non-limiting examples include glass,polycarbonates, acrylics, and the like. In other embodiments, thesubstrate may be flexible, non-limiting examples include polymers,polyesters (e.g., polyethylene terephthalate (PET), polyesternaphthalate, and polycarbonate), polyolefins (e.g., linear, branched,and cyclic polyolefins), polyvinyls (e.g., polyvinyl chloride,polyvinylidene chloride, polyvinyl acetals, polystyrene, polyacrylates,and the like), cellulose ester bases (e.g., cellulose triacetate,cellulose acetate), polysulphones such as polyethersulphone, polyimides,silicones and other conventional polymeric films. In one embodiment, thesubstrate is a polarizer. In one embodiment, the substrate may be thesame material as the coating layer as described above and may furtherinclude contacts extending therethrough as described herein in referenceto the coating layer.

Conductive Plugs

As used herein, conductive plug generally refers to one or moreelectrically conductive features which span the two surfaces of thecoating layer. The conductive plugs are formed, at least in part, fromone or more materials configured to conduct electricity. In someembodiments the conductive material of the plugs are formed from amaterial that is metallic. Suitable metals include, but are not limitedto, silver, gold, copper, nickel, gold-plated silver, platinum andpalladium. The conductive material can also be non-metallic, such ascarbon or graphite (an allotrope of carbon).

As will be explained below, the conductive plugs may be in a liquid,semi-liquid, such as paste, or solid form when provided in the coatinglayer. When in a solid form, the conductive plugs can be of any shape orgeometry. In some embodiments, the conductive plugs are formed into aparticular geometric shape, non-limiting examples spherical,cylindrical, oblong, and the like. When the conductive plugs are appliedin a paste form and used to fill a void in the coating layer as will beexplained below, the conductive plugs may partly or fully fill the shapeof the void. In one embodiment, the conductive plug does not fill thevoid but rather extends along the cross-sectional surfaces of coatinglayer at the perimeter of the void. In one embodiment, the conductiveplugs are conventional flexible connectors having conductive contacts ateach end as is well known in the art. The flexible connectors mayinclude a first contact that is in electrical communication with thenanostructure layer and a second contact that is exposed proximate theouter surface of the coating layer. Non-limiting examples for theflexible connector include flexible printed circuits, wires, springs,and the like.

As indicated above, the size of the conductive plugs may depend on thethickness of the coating layer to allow a portion of the outer surfaceof the conductive plugs to be exposed from the coating layer. Asindicated above, the outer surface of the plugs may extend beyond theouter surface of the coating layer, be flush with the outer surface ofthe coating layer, or remain below the outer surface of the coatinglayer so long as a portion of the outer surface of the plug remainsuncovered by the coating layer.

The plugs may be distributed randomly throughout the coating layer ordistributed at predetermined locations. In some embodiments, a contactarea may be formed in the coating layer to indicate a predeterminedlocation for the plugs. FIG. 5 illustrates structure 500, which issimilar to the structure 400 in FIG. 4, except that the structure 500further includes one or more contact areas 310 formed on the surface ofthe coating layer 102 indicating a predetermined location for one ormore conductive plugs 204. A contact area 310 may be any shape or sizeand more than one conductive plug 204 may be provided in each contactarea 310. The placement of the plugs within each contact area may beregular or irregular, and may also be predetermined or random. In oneembodiment, the contact area 310 is 1 mm² or larger and three or moreconductive plugs 303 are added to each contact area 310. In anotherembodiment, the contact area 310 is a ratio of the size of theconductive plugs 204, such as the contact area 310 may be between 1 to1,000,000 times larger than the individual conductive plugs 204. Forinstance, in one embodiment, there is a single plug 204 which is thesame size as the contact area 310, and in another embodiment, there area plurality of plugs which measure 5 μm and are distributed over thecontact area, which is 1 cm².

Forming Conductive Plugs in the Coating Layer

As discussed above, the structure may include one or more conductiveplugs formed in the coating layer that are configured to electricallycouple the nanostructures in the nanostructure layer to anothercomponent, such as to a ground or an electrical circuit. Such couplingmay be direct, or via another conducting member which is in contact withthe surface of the conductive plug and the circuit or ground to becontacted.

The number of conductive plugs in the coating layer and the distributiontherein may vary. In one embodiment, the number of conductive plugs isany amount that still allows suitable light transmission in the visibleregion (i.e. 400 nm-700 nm) for the structure to be transparent. In oneembodiment, the combination of the coating layer and conductive plugsmay be as a whole able to transmit light that is substantially similarto the light transmission of the nanostructure layer. In otherembodiments, the light transmission of the combination may be any amountthat allows visible light to be transmitted through the layeredstructure such that as a whole the layered structure is substantiallyoptically clear. Thus, in some embodiments, the light transmission ofthe combination may substantially exceed or limit the light transmissionof the nanostructure layer. For instance, in one embodiment, conductiveplugs are distributed along the perimeter of the structure, therebylimiting the transparency of the structure at the perimeter while acenter portion remains suitably transparent. It is to be appreciatedthat the size and/or the quantity of the conductive plugs may reduce thetransparency of the structure.

In some embodiments, the conductive plugs 204 are added to the coatinglayer 102 by first forming voids 402 in the coating layer 102 and laterfilling a portion or all of the voids 402 with conductive material 404thereby forming the conductive plugs 204 as shown in structure 600 inFIGS. 6A and 6B. The structure 600 is similar to the structure 400 inFIG. 4, except that the conductive plugs 204 in structure 600 are formedby filling voids 402 in the coating layer. Various techniques of formingthe voids 402 will be explained in more detail below. In someembodiments, the voids 402 are formed in the contact areas 310 (FIG. 5)of the coating layer 102, while in other embodiments the voids 402 areformed throughout the outer surface 104 of the coating layer 102. Asshown by FIG. 6A, the voids 402 formed in the coating layer extendthrough the thickness of the coating layer 102 exposing a surface areaof the nanostructure layer 110 or conductive film below. The voids mayhave any aspect ratio, and the width of the voids may be similar to,much larger than, or much smaller than the thickness of the coatinglayer. In one embodiment, the exposed surface area of the nanostructurelayer is less than 1% of the contact area.

As indicated above, various techniques may be used to form voids in thecoating layer. In one embodiment, the coating layer is formed during awet deposition or coating process. Upon depositing the coating layermaterial onto the nanostructure layer during the wet deposition process,dewetting may occur, thereby creating voids in the coating layer. Atleast some of the voids may expose a surface area of the nanostructurelayer. In some embodiments, dewetting is encouraged to create more voidsin the coating layer. In general dewetting is favored by use of a highersurface tension solvent for the coating layer and lower surface energyfor the nanostructure layer onto which the coating layer is formed. Theextent of dewetting can be controlled additionally by the viscosity anddrying rate of the coating layer solution. The number of dewetting spotsmay also optionally be controlled by inclusion in the coating layersolution of particles which act as nucleation sites for dewetting, orplacement of such particles on the conductive layer surface before thecoating layer is applied.

In another embodiment, voids are formed in the coating layer during aprinting process, in which the voids are made in the coating layer atparticular locations, such as in the contact areas of the coating layer.Any suitable printing method may be used, such as screen, inkjet,flexographic, gravure, pad, offset, gravure offset, or reverse offsetprinting. Advantageously, printing can provide voids according to apattern to ensure, statistically, enough surface contacts can be madewithin a contact area. Similarly, voids may be made in predeterminedareas. In another embodiment, the coating layer is formed with voidstherein by forming the coating layer with removable plugs. That is, thecoating layer material may be mixed with removable plugs prior tocoating or depositing the coating layer material on the nanostructurelayer. In that regard, as the coating layer material is formed, theremovable plugs are randomly distributed throughout the coating layermaterial. Once the coating layer material is crosslinked or hardened,such as by UV curing, thermal curing, or drying, the removable plugs maybe removed, such as by dissolution, to create voids in the coatinglayer. The removable plugs may comprise water soluble polymers, whichhave limited solubility in the organic solvents commonly used in coatingsolutions (such as esters, ketones, aromatics, fluorinated andchlorinated solvents, and alcohols). For example, a non-ionic polymersuch as hydroxypropyl methyl cellulose, or an ionic polymer such ascarboxymethyl cellulose or poly(acrylic acid) may be used as theremovable plug. The water soluble polymers may be added to the overcoatsolution in the form of dried particles, previously prepared with thedesired particle size by a method such as spray drying, grinding, ormilling, to form a solid particle dispersion. The particle size shouldbe comparable to or larger than the intended dry film thickness of theovercoat, so that when the coating is dry, the plugs extend beyond theouter surface of the overcoat. Alternatively the water soluble polymersmay be added to the overcoat solution in the form of an aqueous polymersolution, which is formed into an inverse emulsion or inverse suspension(sub-micron to micron diameter aqueous droplets suspended in thenon-aqueous coating solvent) through mixing and addition of surfactant.Removal of the water during drying leads to solidification of thesedroplets and formation of plugs. A low molecular weight water-solublesubstance with limited solubility in organic solvents may be usedinstead of a polymer, for example a carbohydrate such as sucrose. If theremovable plug consists of a water soluble polymer, then the plug ispreferably removed from the dry overcoat by rinsing with water todissolve the removable plug.

Although water soluble polymers are preferred as the removable plugs,with water as the dissolving fluid used to remove the plugs, other typesof polymers or low molecular weight substances (including water ororganic solvents) may also be used, as long as they are immiscible withthe main part of the coating solution, and can be selectively removedfrom the dried and cured coating by dissolution or evaporation.

As will be clear to those skilled in the art, the voids in the contactregions made be formed in an initially continuous coating layer by othertechniques, such as laser ablation, plasma treatment, chemical etch, ora mechanical process such as scraping, abrading, cutting, etc. In all ofthese cases, the coating layer may not initially contain voids orprecursors of voids, and coating layer material is selectively removedfrom the contact region by local application of a chemical, physical, orthermal stimulus, to allow contact. In yet another embodiment, thecoating layer may be photosensitive such that when portions of thecoating layer are exposed to light, those portions may be made soluble.If the coating layer comprises a pre-existing solid film material whichis applied to the nanostructure layer, e.g. by lamination, then voids(holes) in the coating layer may be formed prior to its application byany of the above processes. Formation of holes by a punching process orby laser drilling are preferred.

As shown by FIG. 6B, once the voids 402 in the coating layer 102 havebeen formed, one or more of the voids 402 may be completely or partiallyfilled with conductive material 404 to form the conductive plugs 204. Itis to be appreciated that the conductive plugs 204 are coupled to thenanostructure layer 110 or another conductive feature, such asconductive film, and configured to be placed in electrical communicationwith one or more conductive structures in the nanostructure layer 110.As indicated above, the conductive material may be in a liquid,semi-liquid, or solid form and may comprise one or more nanoparticles.In one embodiment, the conductive material is Ag paste. It is to beappreciated that in some embodiments, any number of voids may be filledto establish surface contacts, including only one of many voids formedbeing filled with conductive material.

In one embodiment, the conductive plugs are added to the coating layermaterial prior to depositing the coating layer onto the nanostructurelayer. That is, the conductive plugs are added to the coating layermaterial while in a liquid form. As the coating layer material is coatedor formed onto a surface of the nanostructure layer, the conductiveplugs are randomly distributed across the surface. For example, theconductive plugs may consist of electrically conductive particles thatare mixed with the coating solution.

In other embodiments, the conductive plugs are added to the coatinglayer after coating layer deposition while the coating layer material issoft or displaceable. In one embodiment, prior to hardening the coatinglayer, such as by UV curing, thermal curing, drying, and the like,conductive plugs are added to the coating layer. The conductive plugsmay be added with a force applied, such as gravity by dropping the plugsfrom an elevated height, or by being projected against the coating layerby some other means, such as ejection from a nozzle, or may be moredense than the coating layer material and thus displace the coatinglayer material once placed in contact with it. In one embodiment, theplugs are pushed with a force through at least a portion of the coatinglayer, such as by an applicator or other means. In another embodiment anelectric or magnetic field is used to apply a force to the plugs. In oneembodiment, after applying the coating layer to the layered structurebut before fully hardening the coating layer, the layered structure isstored or otherwise not further processed for anywhere for up to 27weeks prior to including the conductive plugs in the layered structureand fully hardening the coating layer. This advantageously allows thelayered structure to be coated in a first manufacturing process and theconductive plugs to be added to the layered structure in an entirelyseparate manufacturing process.

In certain embodiments, the overcoat is a reflowable polymer. As usedherein, “reflowable polymer” refers to any thermoplastic polymer orcopolymer that becomes pliable above certain temperature and/orpressure, but can return to a solid state upon cooling or release ofpressure. Reflowable polymer may also be softened or dissolved by asolvent, and return to a solid state when the solvent is removed.Reflowable polymers include, without limitation, polyacrylate,polyamide, polyethylene, polyvinyl acetate, polybutylene terephthalate,polyesters, polycarbonate, polyimide, polyurethane, and the like.

A preferred reflowable polymer is poly(methyl methacrylate) (PMMA). PMMAis widely available, relatively inexpensive, transparent, reflowable bymany organic solvents or above a temperature of about 100° C., andprovides environmental protection for silver nanowires. Examples ofother polymers that can be used as a reflowable overcoat include DianalMB 2752, available from Dianal America, Inc. and dissolved powdercoating resins, such as EPON 2002 (a powder coating resin based onbisphenol A/epichlorohydrin epoxy resin), available from MomentiveSpecialty Chemicals Inc., which can be dissolved in, for example,diacetone alcohol.

Reflowable overcoat are preferably in the thickness range of 0.2 to 3μm. For example, if contact is made by silver paste to a nanowire layerthrough a reflowable overcoat, then the reflowable overcoat can besoftened or dissolved by the silver paste solvent, or by the solvent incombination with heat or pressure, providing sufficient flow in theovercoat to allow the Ag particles in the paste to fully penetrate theovercoat and make contact with the underlying nanowire layer. If contactis made by anisotropic conductive film (ACF) bonding, then thereflowable overcoat is melted by the heat involved in ACF bonding, andthe ACF particles can penetrate through the melted overcoat underpressure to make contact with the underlying nanowire layer. Thereflowable overcoat also allows electrical contact to be made by silverpaste or ACF with very low contact resistance, even for very smallcontact pad sizes.

Reflowable overcoats can be applied using any coating or printingmethods including, without limitation, spin coating, slot dye coating,screen printing, in jet printing, gravure printing, flexographicprinting, reverse offset printing and transfer film methods. In applyingPMMA as overcoat, it is preferable to dissolve the PMMA in an organicsolvent such as esters, ketones or aromatics which may, but need not, bemixed with alcohols. In some embodiments, PMMA may be combined withpropylene glycol methyl ether acetate (“PGMEA”) or methyl ethyl ketone(“MEK”) before application.

If a reflowable overcoat is used on a nanowire conductive layer, it maybe advantageous to improve the adhesion between the overcoat and theconductive layer. In some embodiments such adhesion can be improved byincluding adhesion promoters in either the overcoat or the nanowirelayer. In one embodiment, adhesion can be improved by the addition of acrosslinker for one or more binder materials used in the nanowire layer.For example, and without limitation, if a cellulose ester or otherpolymer is used in the nanowire layer, a crosslinker for the celluloseester or other polymer may be added to the overcoat. In one embodiment,HPMC is included as a binder in the nanowire layer and a blockedpolyisocyanate such as Desmodur BL3175A from Bayer Materials Science (atrimer of hexamethylene diisocyanate, blocked with methyl ethyl ketoneoxime), is added to the reflowable overcoat. In one embodiment, a PMMAreflowable overcoat is used and BL3175A is added to the overcoat at alevel higher than about 2% relative to the PMMA and the overcoat iscured for about 15 minutes or more at 150° C. Such overcoat showsimproved adhesion to the nanowire layer when compared to a PMMA overcoatwithout the blocked polyisocyanate or other adhesion promoters. In otherembodiments, other HPMC crosslinkers can be used, such as other blockedor unblocked polyisocyanates, blocked or unblocked melamines, UV curableresins and epoxy compounds. In one embodiment, a UV curable resinincludes HC-5619 UV-curable hard coat from Addison Clearwave Coatings,Inc. An example of a melamine based crosslinker is available from CytecSurface Specialties SA/NV of Belgium under the tradename Cymel® 327. Inanother embodiment, Dianal MB 2752 is used with Desmodur BL3175A as acrosslinker.

In other embodiments, catalysts may also be included in the overcoat toincrease the crosslinking reaction rate and/or lower the required curetemperature. In one embodiment such a catalyst includes dibutyltindilaurate. In another embodiment, Epon 2002, available from MomentiveSpecialty Chemicals, Inc., can be combined with EPIKURE P 101 (animidazole based curing agent for EPON 2002) to form a reflowable coatinglayer.

Reagents may also be included which will cause a direct chemicalreaction between the PMMA and the HPMC at the interface, such as bytransesterification. Exemplary transesterification catalysts include tincompounds (such as dibutyltin dilaurate or dibutyltin oxide) andtitanates such as Tyzor compounds from DuPont.

Adhesion promoters which will improve the adhesion of the nanowire layerto the substrate may also be included within the overcoat or thenanowire layer itself. In one embodiment, if the substrate is glass,then silane coupling agents can be used. If the coupling agents areinitially included in the overcoat (to avoid increasing the complexityor reducing the performance of the nanowire layer), they may diffuse outof the overcoat and through the nanowire layer to the substrate during acure process and form a bond between the substrate and the nanowirelayer.

In other embodiments, PMMA may not be included in a reflowable overcoatfor the nanowire layer. In one embodiment, the overcoat may comprise acopolymer of methyl methacrylate with one or more other monomers (i.e.,co-monomer). Any co-monomer that has a vinyl group is capable of formingco-polymers with methyl methacrylate. In addition to the vinyl group,the co-monomers may contain one or more reactive functional groups.After copolymerization, the reactive functional groups are incorporatedinto the copolymeric overcoat. The reactive function groups can be moreeasily reacted with the functional groups in the constituents of thenanowire binder, such as the hydroxyl groups of HPMC or other celluloseester. Alternatively or in addition, the reactive functional groups ofthe copolymer may crosslink within the overcoat. Examples of thereactive functional groups may be hydroxyl, carboxylic acid, amino,glycidyl and the like.

In certain embodiments, the reflowable overcoat is a polymer orcopolymer based on one or more types of acrylate monomer and/orco-monomer. The acrylate monomer or co-monomer may be represented by thefollowing formula:

wherein, R¹ is hydrogen or alkyl,

L is a direct bond, an alkylene chain, (i.e.,—(CH₂)_(n)—, wherein n is1-10), or an alkylene oxide chain (i.e., —(CH₂)_(m)—O)_(n)—, m is 1-10,n is 1-10);

R² is hydrogen, hydroxyl, amino (including mono-, di-substituted amino),glycidyl, alkyl (substituted or unsubstituted), and aryl (substituted orunsubstituted). The substituents may be halo, hydroxyl, alkyl, amino,aryl, nitro, cyano, haloalkyl, and the like.

In one embodiment, the co-monomer may be a hydroxyl functional monomersuch as hydroxyethyl methacrylate (HEMA), a carboxylate functionalmonomer such as methacrylic acid, an amine monomer such as diethylaminoethyl methacrylate, or an epoxy monomer such as glycidyl methacrylate.Various coupling agents may be used to react each of these functionalgroups with the hydroxyl groups in HPMC or a different reactive group inanother binder polymer. Additionally, even without a coupling reaction,non-covalent interactions of the comonomer with the HPMC hydroxyl groupsmay be sufficient to adequately improve adhesion, such as throughhydrogen bonding interactions.

In other embodiments, the coating layer material may have hardened priorto adding the conductive plugs. For instance, in one embodiment, afterthe coating layer has hardened, at least a portion of the coating layermay later be exposed to heat and/or solvents that cause the coatinglayer to become sufficiently fluid by an amount suitable to insert theconductive plugs as described above. In yet another embodiment,conductive plugs may be heated or exposed to a solvent prior to addingthem to the coating layer. The heated or solvent soaked conductive plugmay be configured to cause a portion of the coating layer to reflow whenthe conductive plug is placed in contact with or pressed against thecoating layer. In this embodiment, the conductive plugs a force may beapplied to assist with causing the coating layer to receive theconductive plug such that the conductive plug makes contact with thenanostructure layer.

After the conductive plug has been inserted into a previously hardenedcoating, which has been softened as described above to allow insertionof the plug, the coating layer may be re-hardened by removal of thesolvent or lowering of the temperature, as will occur if the coatinglayer is a non-crosslinkable thermoplastic polymer. In otherembodiments, the coating layer is crosslinked after the plugs areinserted into the softened coating, such that the coating layer hasimproved hardness, adhesion, or chemical resistance. Suitable coatingmaterials which can be used for this type of process are commonlyavailable for applications such as powder coating, fiber/resincomposites, sealants, and adhesives, and are in some instances known as“B-staged” or “B-stageable” resins. Chemistries suitable for thispurpose include, but are not limited to, acrylate, silicone-epoxy,siloxane, novolac, epoxy, urethane, silsesquioxane, or polyimide Thecrosslinking step may be accomplished by heat, radiation, additionalchemical stimulus, or a combination of these. For example, the coatingmaterial may comprise a solid resin with heat-activated crosslinkingfunctionality; silver paste contacts may be deposited prior tocrosslinking, and crosslinking may be accomplished during the sameheating step used to cure the silver paste contacts, or in a subsequentheating step. Alternatively crosslinking may be accomplished by exposureto UV radiation after electrical contact has been established byinsertion of the conductive plugs.

Turning now to FIG. 7, there is shown a system 700 for formingconductive plugs in the coating layer of a structure in accordance withone embodiment of the present disclosure. The system 700 includes aroll-to-roll processing line for conveying a moving web of film materialthrough various process steps. The film material may include thenanostructure layer and/or the substrate. The system 700 furtherincludes a slot die coating head 504 for depositing the coating layer102 on the first surface 108 of the nanostructure layer 110.

The system 700 further includes a conductive plug applicator 506configured to provide a conductive plug 204 to the outer surface 104 ofthe coating layer 102. In one embodiment, the applicator comprises anozzle for applying drops of a conductive ink or paste. By controllingthe timing of drop deposition relative to the motion of the web, theconductive plugs can be placed with a desired spacing or at a set ofdesired positions. The nozzle may also be moved laterally across theweb, or more than one nozzle may be used at different cross-web ordown-web positions. The nozzle may also be used to form a continuousstraight or curved line of conductive plug material. In anotherembodiment the conductive plug may be a piece of solid conductivematerial, such as e.g. a metal disk or ball, and the applicator placesand applies a force to the conductive plug 204. For example, small/thinmetal discs can be individually positioned on the moving web and pressedagainst it to penetrate the still-soft coating layer layer and makecontact with the nanostructure layer, using, for example, pick and placetooling or the like. In some embodiments, the metal discs deform due tothe force being applied such that a portion, such as a center portion,makes contact with the nanostructure layer and the side portions formalong the sidewalls of a void formed in the coating layer. As describedabove, the conductive plug 204 displaces the flowable coating layer 102and makes physical contact with the nanostructure layer 110 or theconductive bonding material therebetween. In the illustrated embodiment,the system 700 further includes a dryer 508 and a UV cure lamp 510configured to harden the coating layer. It is to be appreciated,however, that the type of technique (including air drying) used to causethe coating layer 102 material to harden will depend on the type ofmaterial used for the coating layer. In another embodiment, the coatinglayer 102 may go through a drying or UV curing prior to adding the plugsso long as the plug displaces the coating layer material sufficient tomake contact with the nanostructure layer or the conductive bondingmaterial below.

Turning now to 8, there is shown a schematic of a display, such as anLCD device 800. A backlight 804 projects light through a bottomsubstrate 812. The bottom substrate 812 may be a glass substrate, apolarizer, or a combination thereof. A plurality of first transparentconductor strips 820 are positioned between the bottom substrate 812 anda first alignment layer 822. The first transparent conductor strips 820may form the conductive nanostructure layer. Each transparent conductorstrip 520 alternates with a data line 824. The first alignment layer 822may be a coating layer and have one or more conductive plug 826 formedtherein.

Spacers 830 are provided between the first alignment layer 822 and asecond alignment layer 832, the alignment layers sandwiching liquidcrystals 836 in between. The second alignment layer 832 may be a coatinglayer and have one or more conductive plug 826 formed therein. Aplurality of second transparent conductor strips 840 are positioned onthe second alignment layer 832, the second transparent conductor strips840 orienting at a right angle from the first transparent conductorstrips 820.

The second transparent conductor strips 840 may be further coated with apassivation layer 844, colored matrices 848, a top glass substrate 850and a polarizer 854. The transparent conductor strips 820 and 840 can bepatterned and transferred in a laminating process onto the bottomsubstrate, and the alignment layer, respectively. Unlike theconventionally employed metal oxide strips (ITO), no costly depositionor etching processes are required.

Turning now to FIG. 9, there is shown a schematic illustration of aresistive touch screen device 640. The device 640 includes a bottompanel 642 and an upper panel 650. The bottom panel 642 comprises alayered structure that includes a first substrate 644 coated orlaminated with a first conductive layer 646, and a first coating layer647 thereon. The first coating layer 647 has one or more conductiveplugs 626 therein. The upper panel 650 includes a layered structure thatincludes a second conductive layer 654 coated or laminated on a secondsubstrate 656, and a second coating layer 655 thereon. The secondcoating layer 655 has one or more conductive plugs 626 therein. Althoughonly a few conductive plugs 626 are shown, it is to be understood thatthe first and second coating layers 647 and 655 may include moreconductive plugs than are illustrated.

The upper panel 650 is positioned opposite from the bottom panel 642 andseparated therefrom by adhesive enclosures 652 and 652′ at respectiveends of the device 640. A surface of the conductive plugs 626 in thefirst coating layer 647 face a surface of the conductive plugs 626 inthe second coating layer 655 which may be suspended over spacers 660.

When a user touches the upper panel 650, the conductive plugs 626 of thesecond coating layer 655 in the top panel 650 and the conductive plugsof the first coating layer in the bottom panel 642 come into electricalcontact. A contact resistance is created, which causes a change in theelectrostatic field. A controller (not shown) senses the change andresolves the actual touch coordinate, which information is then passedto an operating system. Spacers 626 can also or alternatively be used toconnect conductive layers 646 and 654 to external driving circuitry.

According to this embodiment, either or both first and second conductivelayers are based on conductive nanowire layers, as described herein. Thesurface of the first and second coating layers 647 and 655 may each havea surface resistivity in the range of about 10-1000Ω/□, more preferably,about 10-500Ω/□. Optically, the upper and bottom panels may have hightransmission (e.g., >85%) to allow for images to transmit through.

FIGS. 13A-13D illustrate another embodiment of a method of forming acontact to a conductive layer through an overcoat. In FIG. 13A, asubstrate 950 is coated with a conductive layer 952 that may includeconductive nanostructures as disclosed herein.

Thereafter, as shown in FIG. 13B, a first electrical contact 954 isdeposited on conductive layer 952. Contact 954 can be formed of anymaterial, including those for forming a conductive plug as disclosedherein. The contact may be deposited in a liquid, semi-liquid, or solidform. In certain embodiments, the contact may comprise one or morenanoparticles and may be deposited or spot-deposited by as part of aprocess in a coating line for example through a nozzle as discussedherein or any other suitable method, including ink jet printing, screenprinting and the like. The conductive contacts may be formed at randomor predetermined locations of the conductive layer.

In FIG. 13C, an overcoat layer 956 is applied over the conductive layer952 and contact 954. Overcoat layer 956 may be formed of any overcoatmaterial discussed herein, including a reflowable material. In certainembodiments, a liquid overcoat material may be coated over theconductive layer 952 and cured (e.g., UV-cured) or hardened (e.g., bysolvent evaporation) to form the overcoat layer 956. In otherembodiments, the overcoat layer 956 may also be a protect film or othertype of functional layer that is placed over and adhered to conductivelayer 952.

Thereafter, as shown in FIG. 13D, a via hole 958 is formed into overcoatlayer 956 above contact 954 to allow electrical contact from above theovercoat layer to conductive layer 952 by means of the first electricalcontact. Via hole 958 is preferably formed by laser ablation but may beformed by other methods including any other methods disclosed hereinsuch as plasma treatment, chemical etch, or a mechanical process such asscraping, abrading, cutting, mechanical drilling, etc. For example, ifthe overcoat layer 956 is a film layer, via hold 958 may be precut inthe film.

If the via hole is formed by laser ablation, then the wavelength of thelaser should preferably be chosen to coincide with the infrared or UVabsorption spectrum of the overcoat (which is preferably non-absorbingin the visible range). For example, carbon dioxide (CO₂) lasers emitinfrared light in the 9-11 micron wavelength range, which corresponds tostrong absorption in many acrylic polymers, and are commonly used forcutting and drilling of acrylic.

It is also considered to make electrical contact to contact 954 withouta process step specifically to form a via hole. For example, theovercoat layer 956 may at least partially de-wet in the region ofcontact 954. Overcoat layer 956 may also be at least partially absorbedinto voids in contact 954 leaving the contact exposed. Alternately, ifthe overcoat layer 956 is cross-linked and electrical contact is made tocontact 954 using heat and pressure (such as in wire bonding or ACFbonding), the overcoat layer 956 may fracture, allowing electricalcontact to be made.

As shown in FIG. 13E, electrical contact to contact 954 through via hole958 can be made in many different ways, including but not limited toattachment of a wire 960 or other conductor to the first contact bymeans of conductive adhesive, solder, or bonding with heat, pressure, orultrasound. Wire 960 or other contact may be in electrical communicationwith an external circuit or ground.

Various embodiments for forming the nanostructures (nanowires) andnanostructure layers described herein are further illustrated by thefollowing non-limiting examples.

EXAMPLES Example 1 Synthesis of Silver Nanowires

Silver nanowires may be synthesized by a “polyol” process in which asilver precursor (e.g. a silver salt such as silver nitrate) is reducedto silver in ethylene glycol in the presence of poly(vinyl pyrrolidone)(PVP). The polyol method is generically described in, e.g., Y. Sun, B.Gates, B. Mayers, & Y. Xia, “Crystalline silver nanowires by softsolution processing,” Nanoletters 2(2): 165-168, 3002. The polyolprocess may be modified to better control for the resulting nanowiremorphology, including wire diameter, length and aspect ratio. Examplesof these modified polyol syntheses are described in U.S. Pat. Nos.8,709,125, 8,512,438, 8,541,098, U.S. Published Application No.2011/0174190, and U.S. patent application Ser. No. 14/684,313, all inthe name of Cambrios Technology Corporation, which are incorporated byreference herein in their entireties. In certain embodiments, thenanowires primarily were about 13 μm to about 17 μm long and about 34 nmto about 44 nm in diameters. In other embodiments in which thinner wiresare preferred, the nanowires were primarily 12 μm to about 20 μm andabout 15 nm to 30 nm in diameters.

Example 2 Standard Preparation of Coating Composition of ConductiveNanostructures

A typical coating composition for depositing metal nanowires comprises,by weight, from 0.0025% to 0.1% surfactant (e.g., a preferred range isfrom 0.0025% to 0.05% for ZONYL® FSO-100), from 0.02% to 4% viscositymodifier (e.g., a preferred range is 0.02% to 0.5% for hydroxypropylmethylcellulose (HPMC), from 94.5% to 99.0% solvent and from 0.05% to1.4% metal nanowires.

The coating composition can be prepared based on a desired concentrationof the nanowires, which is an index of the loading density of the finalconductive film formed on the substrate.

The coating composition can be deposited on a substrate according to,for example, the methods described in co-pending U.S. patent applicationSer. No. 11/504,822.

As understood by one skilled in the art, other deposition techniques canbe employed, e.g., sedimentation flow metered by a narrow channel, dieflow, flow on an incline, slit coating, gravure coating, microgravurecoating, bead coating, dip coating, slot die coating, and the like.Printing techniques can also be used to directly print an inkcomposition onto a substrate with or without a pattern. For example,inkjet, flexoprinting and screen printing can be employed. It is furtherunderstood that the viscosity and shear behavior of the fluid as well asthe interactions between the nanowires may affect the distribution andinterconnectivity of the nanowires deposited.

A sample conductive nanostructure dispersion was prepared that comprisedsilver nanowires as fabricated in Example 1 dispersed, a surfactant(e.g., Triton), and a viscosity modifier (e.g., low molecular-weightHPMC) and water. The final dispersion included about 0.4% silver and0.4% HPMC (by weight). This dispersion can be used (neat or diluted) incombination with a light-scattering material (e.g., in a particulateform) directly to form a coating solution. Alternatively, the dispersioncan be combined with a dispersion of a light-scattering material to forma coating solution.

Example 3 ACF Contact Through Thick Thermoplastic Overcoat

A transparent conductive layer with a thermoplastic overcoat wasprepared as follows. An ink was prepared containing 0.4 wt % silvernanowires, 0.4% HPMC (Methocel K100), and 250 ppm surfactant (Triton×100). The ink was coated onto 2″ square pieces of clean glass (EagleXG) by spin coating at 1000 rpm, drying at 50 degrees C. for 90 seconds,and baking at 140 degrees C. for 90 seconds, resulting in a coating witha sheet resistance of 14 ohms/square. PMMA (MW=120,000 gm/mol) wasdissolved in PGMEA at a concentration of 5%, 10%, or 15%, and coated atspin speeds of 500 and 1000 rpm, in each case for 30 seconds. Thesamples with overcoat layer were dried at 50 degrees C. for 90 seconds,then baked at 140 degrees C. for 10 minutes to remove the solvent andanneal the film. After baking, the overcoat forms a hard, solid,transparent layer. There was no change in the sheet resistance afterapplying the overcoat, as measured by a non-contact technique; howeverafter applying the overcoat, it was no longer possible to makeelectrical contact to the conductive layer with probes, due to thepresence of the overcoat. The overcoat thicknesses for the differentconcentration/spin speed combinations were determined by preparingsimilar PMMA coatings on glass (without a nanowire layer) and measuringthe thickness with a KLA Tencor AlphaStep profilometer.

ACF bonding was done using Sony CP8016K-45AC anisotropic conductingadhesive tape. The tape contains 6 μm diameter solid nickel particles.The bonding conditions were a peak temperature of 182 degrees C., abonding time of 10 seconds at the peak temperature, and a pressure inthe range 3-6 MPa (variable between experiments). The bond was madebetween the unpatterned overcoat/nanostructure film, and a flexibleprinted circuit (FPC) connector with 80 μm wide contact pads spaced at a140 μm pitch. The contact pads were 18 μm thick copper with Ni/Auplating. In this example, the individual ACF particles comprise‘conductive plugs’, and the area of each contact comprises the ‘contactarea’.

The bonds were electrically characterized by using a multimeter tomeasure the two-point resistance between adjacent probe points on theFPC, such that the current from the meter passes through one contactinto the transparent conducting layer, then out of the transparentconducting layer through the other contact. The measured resistanceincludes the test leads, FPC connector, contact resistances, and theresistance of the transparent conductor. values for the two-pointresistances for different samples are reported in table 1. For overcoatthickness from 0 to 900 nm, the two-point resistances are all below 10ohms, and there is very little increase in Rc with increasing overcoatthickness. At 1.8 μm thickness, the two-point resistances are mostlybetween 10 and 100 ohms, with some reading >1 kOhm; and at 2.6 μmthickness, the two-point resistances are mostly in the hundreds of ohms,again with some reading >1 kOhm. The resistance is consistently higherbetween pads 5-6 due to a larger distance between the contacts, and theconsistently higher resistances between pins 1-2 and 2-3 may indicate ananomaly in the bond head or the FPCs at position 2 (such as unevenpressure).

To try to improve the contact with a 2.6 μm thick overcoat, the bondingconditions were modified. Higher pressure was used (4 or 5 MPa), and thetemperature ramp rate (from RT to the bonding temperature) was sloweddown to provide a longer time interval above the glass transitiontemperature of PMMA before curing of the ACF adhesive, to give the ACFparticles more time to move through the thicker overcoat and come incontact with the nanostructure layer. The results show that it ispossible to further improve the contact with a thicker thermoplasticovercoat by modifying the process conditions.

TABLE 1 Two-point resistances for different samples Sam- Spin ple Wt %Speed, Overcoat Process Two-point resistance, Ohms # PMMA rpm thicknesscomments pins 1-2 pins 2-3 pins 3-4 pins 4-5 pins 5-6 pins 6-7 pins 7-8pins 8-9 pins 9-10 1 NA NA NA 3 75,000 3 3 14 3 3 3 3 2  5% 1000 200 nm3 3 3 3 13 3 3 3 3 3  5% 500 300 nm 4 4 4 4 15 4 4 4 4 4 10% 1000 600 nm11K OL 5 5 18 4 5 4 4 5 10% 500 900 nm 8 OL 7 6 22 5 7 7 5 6 15% 10001.8 um 30 41 17,000 33 58 26 33 39 5,500 7 15% 500 2.6 um 2,400,0001,200 47 4,200 87 4,650 248 117 608 8 15% 500 2.6 um P = 4 MPa 580,00354 269 113,000 730,000 5,000 10,500 209 186 9 15% 500 2.6 um P = 5 MPa20,300 59,500 500,000 212 850 127 40 285 295 10 15% 500 2.6 um Slow 34155 351 353 110 238 122 248 116 ramp, 5 MPa 11 15% 500 2.6 um Slow 6571,340 279 255 1,790 2,2

0 6,030 856 826 ramp, 6 MPa

indicates data missing or illegible when filed

Example 4 Ag Paste Contact Through a Thick Thermoplastic Overcoat

A transparent conductive layer with a thermoplastic overcoat wasprepared as follows. An ink was prepared containing 0.1 wt % silvernanowires, 0.2% HPMC (Methocel K100), and 250 ppm surfactant (Triton×100). The ink was coated onto 4″ square pieces of clean glass (EagleXG) by spin coating at 750 rpm, drying at 50 degrees C. for 90 seconds,and baking at 140 degrees C. for 90 seconds, resulting in a coating witha sheet resistance of approximately 150 ohms/square. PMMA (MW=120,000gm/mol) was dissolved in PGMEA at a concentration of 5%, 7.5%, 10%, and15%, and coated at various spin speeds, in each case for 30 seconds. Thesamples with overcoat layer were dried at 50 degrees C. for 90 seconds,then baked at 110 degrees C. for 5 minutes to remove solvent and annealthe overcoat. There was no change in the sheet resistance after applyingthe overcoat, as measured by a non-contact technique; however afterapplying the overcoat, it was no longer possible to make electricalcontact to the conductive layer with probes, due to the presence of theovercoat. The overcoat thicknesses for the different concentration/spinspeed combinations were determined by preparing similar PMMA coatings onglass and measuring the thickness with a KLA Tencor AlphaStepprofilometer.

Silver paste contacts were formed on the coated substrates as follows.The paste used was Toyobo DW-117H-41T05. Pairs of rectangular Ag pastecontacts were printed, with the individual contacts measuring 1×2 mm²,2×4 mm², or 4×8 mm². Six contact pairs of each size were printed on eachsubstrate (18 pairs total), as shown in FIG. 9. A stainless steel 250mesh screen with a 0.0005″ thick emulsion was used for screen printing.The distance between the two contacts in a pair is varied proportionallyto the size of the contacts in that pair, and if the contact resistanceis negligible, then the two-point resistance comes primarily from thenanowire layer and is independent of the pad size. After printing, thesamples were baked in a convection oven at 130 degrees C. for 30 minutesto cure the silver paste and allow them to penetrate through theovercoat. After curing and cooling the samples, the resistance wasmeasured for all pairs of same-sized contacts, and the results are shownin Table 2. The data show that electrical contact can be made eventhrough a 2.5 μm thick PMMA overcoat, with only a small amount ofcontact resistance increase for the thickest overcoats and smallestcontact pads.

FIG. 9 illustrates contact pad layout for Example 4. The smallrectangles are the silver paste pads, deposited by screen printing. Thetwo-point resistance is measured for pairs of adjacent same-sized pads.Numbers indicate contact ‘group’ number, the six groups are replicates(same sized pads and distances). Pad sizes 4×8, 2×4, 1×2, and 0.5×1 mm².0.5×1 mm² pads are difficult to measure manually and data were notrecorded.

TABLE 2 Resistance was measured for all pairs of same-sized contactsContact pad dimensions PMMA thickness (nm) Pair # (mm × mm) 200 400 600800 1000 1500 2000 2500 1 1 × 2 63.8 68.6 69.0 69.3 69.7 79.2 79.7 93.22 1 × 2 71.8 83.0 78.7 77.8 77.3 78.3 88.3 100.4 3 1 × 2 71.6 79.2 78.279.0 77.5 79.3 94.0 122.0 4 1 × 2 60.3 64.5 69.1 69.4 69.8 72.6 95220.084.5 5 1 × 2 61.9 59.5 81.8 74.3 79.0 84.3 94.3 97.6 6 1 × 2 62.0 62.268.8 59.2 66.3 64.9 72.7 88.7 1 2 × 4 62.3 68.5 68.8 65.7 63.4 67.4 68.574.2 2 2 × 4 73.2 78.3 75.6 73.7 75.2 76.2 79.1 84.3 3 2 × 4 66.0 69.468.3 69.4 68.1 72.3 74.7 82.8 4 2 × 4 56.2 59.1 66.7 60.5 62.9 60.8 64.267.7 5 2 × 4 62.5 60.6 62.4 62.2 71.7 70.1 67.8 73.5 6 2 × 4 60.0 58.960.6 57.6 59.7 58.2 62.8 70.5 1 4 × 8 59.4 62.5 62.7 59.4 61.9 62.4 64.864.8 2 4 × 8 69.9 76.9 73.0 73.3 70.7 74.7 74.9 78.9 3 4 × 8 64.2 66.363.8 62.3 62.0 67.6 66.9 70.1 4 4 × 8 67.4 67.2 70.4 67.0 68.7 69.7 71.273.7 5 4 × 8 70.8 72.5 78.7 70.8 75.5 73.6 73.5 78.4 6 4 × 8 63.4 62.064.2 62.0 63.4 64.3 75.1 68.6

Numbers in the main part of the table are two-point resistance in ohms.

Example 5 Contact Through a Thick Layer of Un-Cured Overcoat, Followedby UV Curing

A silver nanowire ink was prepared containing 0.1% silver nanowires,0.2% HPMC (Methocel K100), and 250 ppm surfactant (Triton ×100). The inkwas spin coated at 750 rpm for 60 seconds onto 2″ square pieces of cleansoda lime glass. After spin coating, the nanowire layer was dried for 90seconds at 50 degrees C. and then baked at 140 degrees C. for 90seconds. An overcoat coating solution was prepared consisting of 40 wt %Addison Clearwave HC-5619 [a UV-curable acrylic coating] in a 50:50mixture of isopropyl alcohol and diacetone alcohol. The overcoat wasdeposited on top of the nanowire layer by spin coating at 600 rpm for 10seconds. The overcoated samples were dried at 50 degrees C. for 4minutes and 130 degrees C. for 2 minutes.

In a comparative example, the overcoat was then cured by passing itthree times through a Fusion UV curing system, with an H-bulb lightsource and a belt speed of 20 feet per minute. The total UV exposureafter three passes (UVA+UVB) was approximately 3.6 J/cm². After curingthe overcoat was clear, dry, and hard, and could be rubbed vigorouslywith an alcohol-soaked wipe without damage. Toyobo DW-117H-41T05 silverpaste was mixed with dibasic esters at a ratio of 1.3:1, and drops ofthe diluted paste were manually applied to the surface of the UV-curedovercoat, a few millimeters away from the edges of the substrates. Theindividual drops were well separated from each other and not in mutualphysical contact. The silver paste was then cured by baking at 130degrees C. for 30 minutes in a convection oven.

In an inventive version of the above example, the above procedures werealso followed, except that UV curing was done after application of thesilver paste, instead of before. In other words, the silver paste wasapplied to the surface of an overcoat layer which had been dried, butnot yet UV cured.

The sheet resistance after coating and baking of the nanowires wasmeasured as approximately 95-100 ohms/square for all samples, asmeasured by a Delcom non-contact sheet resistance meter. After UV curingof the overcoat, the non-contact sheet resistance for all samples wasincreased to approximately 130-140 ohms/square. For the samples preparedby the method of the comparative example, all of the silver pastecontacts were electrically isolated from one another. This wasdemonstrated by contacting pairs of silver paste contacts with probesand measuring the electrical resistance. The resistance was off scale(not measurable) for all pairs tested. For the inventive example, bycontrast, all pairs of silver paste contacts were electrically connectedto each other, with a typical two-point resistance of 160-180 ohms.Since the contacts were physically separated from each other, it can beinferred that electrical contact between the contacts took place throughthe nanostructure layer, which was in electrical communication with thecontacts.

Samples from both the inventive and comparative examples were eachfractured through one of the electrical contacts, and a cross sectionwas examined in a scanning electron microscope. In the comparativeexample, it was seen that the silver paste sits on top of the overcoatand is not in physical contact with substrate surface, where thenanowire layer is located. In the inventive example, it can be seen thatthe silver paste has penetrated and/or mixed with the overcoat, and isin physical contact with the substrate surface where the nanowire layeris located.

Example 6 Contact with Thick Laminate Covering Layer

Preparation of transparent conducting films for Example 6. Transparentconductive nanostructures layer was prepared as follows. The inkcomposition was 0.1% Ag nanowires, 0.2% HPMC (Methocel K100), and 250ppm Triton ×100. The ink was spin coated onto 4″ square pieces of PETfilm (125 μm thick, no hardcoat) at 500 rpm. The films were taped to apiece of glass for spin coating. After spin, the samples were allowed toair dry for 5 minutes, then were baked in an oven at 100 degrees C. for10 minutes. The non-contact sheet resistance for all samples wasmeasured and was between 90 and 100 ohms/sq.

Example 6a. To one of the nanowire/PET films 910 prepared as above,three silver paint contacts (Pelco colloidal silver) 912 were appliedmanually as shown in FIG. 11A. The contact diameter was between 0.5-1cm. The contacts were dried in a 100 degrees C. oven for 30 minutes. Thefilm was then removed from the glass carrier. A 3″×5″ piece of PET film914, with optically clear adhesive and protect film, was prepared. Withthe protect film still in place, three square holes 916 were cut in thefilm with a razor blade as shown in FIG. 11B. The size of the holes wasapproximately 5 mm. The protect film was then removed, and the laminatecover layer with holes was laminated to the NW/PET film as shown in FIG.11C, using a rubber roller. The previously applied Ag paint contactswere completely covered by the laminated film.

After lamination, the film was cut with the cut line 918 passing throughthe previously applied Ag paint contacts, which are hereafter referredto as ‘buried contacts’. Then additional Ag paint contacts were appliedas shown in FIG. 11D. The contacts are divided into groups as follows:

Group 1: Ag paint is in physical contact with the surface of thenanowire layer, the edge of the laminate film, and the top surface ofthe laminate film.

Group 2: Ag paint is applied over the square holes in the laminate film,so that Ag paint is in physical contact with the surface of the nanowirelayer exposed by the hole, the edges of the holes in the laminate film,and the top surface of the laminate film.

Group 3: applied to the surface of the laminate film, away from alledges and holes.

Group 4: applied to the cut edge of the laminate/PET bilayer and theadjacent top surface of the laminate layer, so that each Ag paintdeposit wraps around the corner and is in contact with both the edge andtop surface. Contacts 4A, 4C, and 4E were applied at the positions ofthe ‘buried’ Ag paste contacts, while contacts 4B, 4D, and 4F wereapplied at positions where there were no buried Ag paste contacts.

After applying the additional contacts, the film was dried at 70 degreesC. for 15 minutes. Then the electrical resistance between contact 1A andall other contacts was measured pair-wise with a multimeter and probes.In all cases the probe was placed in contact with the Ag paint on thetop surface of the laminate film, not on the edges or on the exposednanowire layer. The results show that all contacts in groups 1 and 2 arein mutual electrical contact and therefore in contact with thenanostructure layer; the contacts in group 3 are electrically isolatedfrom the nanostructure layer; and the edge contacts in group 4 areeither in contact with or isolated from the nanostructure layer,depending on whether they are applied adjacent to one of the ‘buried’ Agpaint contacts or not, respectively.

The occurrence of electrical contact for edge contacts depositedadjacent to buried contacts can have two causes. 1) The edge contact canbe in direct electrical contact with the edge of the buried contact,which was exposed by cutting; and/or 2) the edge contact can be indirect contact with the nanostructure layer, via a gap between thenanowire layer and the laminate film caused by the finite thickness ofthe edge contact. To determine whether the second mechanism waspossible, Example 6b was performed.

Example 6b. To one of the nanowire/PET films 910 prepared as above,three silver paint contacts (Pelco colloidal silver) 912 were appliedmanually as shown in FIG. 12A. The contact diameter was between 0.5-1cm. The contacts were dried in a 100 degrees C. oven for 30 minutes.Narrow strips of adhesive-coated PET 920 were also applied to anotherpart of the film.

The film was then removed from the glass carrier. In reference to FIG.12B, 3″×5″ piece of PET film 914, with optically clear adhesive andprotect film, was prepared. With the protect film still in place, threesquare holes 916 were cut in the film with a razor blade. The size ofthe holes was approximately 5 mm. The protect film was then removed, andthe laminate cover layer with holes was laminated to the NW/PET film asshown in FIG. 12C, using a rubber roller. The previously applied Agpaint contacts were completely covered by the laminated film, and thepreviously applied PET/adhesive strips were partly covered.

After lamination, the film was cut, with one cutting line 918 passingthrough the previously applied Ag paint contacts, which are hereafterreferred to as ‘buried contacts’, and a second cutting line 922 passingthrough the buried PET strips, which will hereafter be referred to as‘buried spacers’. Then additional Ag paint contacts were applied asshown in FIG. 12D. The contacts are divided into groups as follows:

Group 1: Edge/surface contacts, similar to Group 4 in Example 4A.Contacts 1A, 1C, and 1E were applied adjacent to the buried spacers,while contacts 1B, 1D, and 1F were not in contact with the buriedspacers.

Group 2: As in example 4A.

Group 3: As in example 4A.

Group 4: As in example 4A.

After applying the additional contacts, the film was dried at 70 degreesC. for 15 minutes. Then the electrical resistance between contact 2A andall other contacts was measured pair-wise with a multimeter and probes.In all cases the probes were placed in contact with the Ag paint on thetop surface of the laminate film. The results for groups 2, 3, and 4 aresimilar to Example 6A. In Group 1, two of the edge contacts adjacent tothe buried spacers are in electrical contact with the nanostructurelayer, while the edge contacts not adjacent to buried spacers are allelectrically isolated. This indicates that an electrically insulating‘buried spacer’ can also enable electrical contact between Ag paint andthe nanostructure layer, possibly by opening up a gap between thenanostructure layer and the laminate film at the edge of the sample intowhich the Ag paint can flow.

Example 7 Edge Contact with a Thick UV-Cured Overcoat

A thick UV-cured overcoat layer was formed on a transparent conductivenanowire film as follows. The starting film (ClearOhm, Cambrios) hadsheet resistance of 130 ohms/square and a 130 nm thick UV-curedovercoat. The substrate was 125 μm thick PET. The 130 nm overcoat layeris sufficiently thin such that electrical contact can be made. Anadditional thick UV-cured overcoat layer was coated on top as follows. Apiece of the film was taped to a glass sheet for spin coating. A 40 wt %solution of HC-5619 in a 1:1 mixture of diacetone alcohol/isopropylalcohol was spin coated on top of the film at 600 rpm for 10 seconds.The film was then dried for 1 minute on a hotplate at 50 degrees C.,baked for 1 minute in an oven at 130 degrees C., and was then UV curedwith the same equipment and process described in Example 3. Then thefilm was removed from the glass carrier by cutting away the taped edgeswith a razor blade.

Silver paint contacts (Pelco colloidal silver) were then applied to theedges of the sample (five contacts per edge or twenty edge contactstotal). The edge contacts also extended to the top surface as in theprevious examples. Ten contacts were also applied to the surface of theovercoat in the center of the film, away from the edges. The resistancebetween pairs of contacts was measured with a multimeter and probes. Itwas found that all edge contacts were in electrical contact with eachother, with typical two-probe resistance of 500-700 ohms; and none ofthe top contacts was in electrical contact with each other or with anyof the edge contacts. Since all contacts are physically isolated fromeach other, it can be concluded that all of the edge contacts and noneof the surface contacts are in electrical contact with the nanowirelayer.

Example 8 Increased Adhesion Overcoat Using Blocked Isocyanate

A transparent conductive layer with a thermoplastic overcoat wasprepared as follows. An ink was prepared containing 0.15 wt % silvernanowires, 0.3% HPMC (Methocel K100), and 250 ppm surfactant (Triton×100). The ink was coated onto 5 4″×4″ hardcoat PET substrates by spincoating at 1000 rpm. The films were dried at 50 degrees C. for 90seconds, and baked at 140 degrees C. for 90 seconds, resulting incoatings with a sheet resistance of approximately 150 ohms/square. PMMA(MW=120,000 gm/mol) was dissolved in PGMEA at a concentration of 7.5%and the solutions further comprised 0%, 1%, 2.5%, 5% and 10% DesmodurBL3175A relative to the PMMA. Each Desmodur/PMMA/PGMEA combination wasspin coated at 1000 rpm for 60 seconds onto the separate nanowire layersto produce overcoats of approximately 400 nm thickness. The samples weredried at 50 degrees C. for 90 seconds, then baked at 110 degrees C. forup to 15 minutes. A tape test similar to that described in ASTM 3359-02was carried out on each sample. According to ASTM D 3359-02, a cross cuttool was used to prepare vertical and horizontal parallel cuts on thesample surface to make a cross hatch pattern. A pressure sensitive tapewas then applied on the cross hatch pattern and pressure was applied toflatten the tape by using rubber erased on the back of a pencil. Thetape was then peeled off after waiting for 90 seconds by pulling it offrapidly back over itself as close to an angle of 180°. The film surfacewas then inspected by microscope to see if any portion of the coatingwas peeled off in the test. If some portion of the coating is removed bythe tape, the sample ‘fails’ the test. If no portion of the scoredcoating is removed, the sample ‘passes’. The samples including 0%, 1%and 2.5% Desmodur BL3175A relative to the PMMA failed the tape test andthe samples including 5% and 10% Desmodur BL3175A relative to the PMMApassed the tape test. This demonstrates improved adhesion when usingamounts of the blocked polyisocyanate in excess of 5% relative to thePMMA.

Example 9 Increased Adhesion Overcoat Using UV Curable Resin

A transparent conductive layer with a thermoplastic overcoat wasprepared as follows. An ink was prepared containing 0.1 wt % silvernanowires, 0.2% HPMC (Methocel K100), and 250 ppm surfactant (Triton×100). The ink was coated onto four, 4″×4″ single side hardcoat PETsubstrate (substrates were taped to 5″×5″ soda lime glass for spincoating using polyimide tape, ink coating was on the non-hard coatedside) by spin coating at 750 rpm for 60 seconds. The film was then driedat 50 degrees C. for 90 seconds, and baked at 140 degrees C. for 90seconds, resulting in a coating with a sheet resistance of approximately150 ohms/square.

PMMA (MW=120,000 gm/mol) was dissolved in PGMEA at a concentration of 15wt %. HC-5619, available from Addison Clearwave Coatings, Inc., wasdissolved in PGMEA at concentration of 15 wt %. The two solutions weremixed quantitatively to achieve solutions containing 10%, 20%, and 80%HC-5619 relative to the PMMA. The final blended solutions were at aconcentration of 15 wt % solids in PGMEA.

Each HC-5619/PMMA solution in PGMEA was spin coated at 1000 rpm for 60seconds onto separate 4″×4″ single side hardcoat PET substrate coatedwith nanowire layers previously (as mentioned in the above paragraph) toproduce overcoats of approximately 2 μm thickness. The samples weredried at 50 degrees C. for 90 seconds, and then baked at 100 degrees C.for up to 10 minutes. The samples were then cured by exposing them to UVradiation under nitrogen blanket using Fusion UV system (model: DRS 120)installed with H-Bulb (UVA+UVB dose=1.6 J/cm²) to achieve a non-tacky,crosslinked overcoat film.

A tape test similar to that described in ASTM D 3359-02 was carried outon each sample. According to ASTM D 3359-02, a cross cut tool was usedto prepare vertical and horizontal parallel cuts on the sample surfaceto make a cross hatch pattern. A pressure sensitive tape was thenapplied on the cross hatch pattern and pressure was applied to flattenthe tape by using rubber erased on the back of a pencil.

The tape was then peeled off after waiting for 90 seconds by pulling itoff rapidly back over itself as close to an angle of 180°. The filmsurface was then inspected by microscope to see if any portion of thecoating was peeled off in the test. If some portion of the coating isremoved by the tape, the sample ‘fails’ the test. If no portion of thescored coating is removed, the sample ‘passes’. The samples including10%, 20% HC-5619 with respect to PMMA passed the tape test with nopeeling of the coating demonstrating improvement in PMMA overcoatadhesion when 10-20% HC-5619 was added in the formulation. The samplewith 80% HC-5619 with respect to PMMA failed the tape test.

Example 10 Increased Overcoat Adhesion Using Melamine Based Crosslinker

A transparent conductive layer with a thermoplastic overcoat wasprepared as follows. An ink was prepared containing 0.1 wt % silvernanowires, 0.2% HPMC (Methocel K100), and 250 ppm surfactant (Triton×100). The ink was coated onto two, 4″×4″ single side hardcoat PETsubstrate (substrates were taped to 5″×5″ soda lime glass for spincoating using polyimide tape, ink coating was on the non-hard coatedside) by spin coating at 750 rpm for 60 seconds. The film was then driedat 50 degrees C. for 90 seconds, and baked at 140 degrees C. for 90seconds, resulting in a coating with a sheet resistance of approximately150 ohms/square.

PMMA (MW=120,000 gm/mol) was dissolved in PGMEA at a concentration of 15wt %. Cymel 327 was used as supplied (90 wt % non-volatiles inisobutanol). Cymel 327 was added quantitatively to achieve solutionscontaining 5%, and 10% Cymel 327 relative to the PMMA.

Each PMMA/Cymel 327 solution in PGMEA was spin coated at 1000 rpm for 60seconds onto separate 4″×4″ single side hardcoat PET substrate coatedwith nanowire layers previously (as mentioned in the above paragraph) toproduce overcoats of approximately 2 μm thickness. The samples weredried at 50 degrees C. for 90 seconds, baked at 100 degrees C. for up to10 minutes and then cured at 130 C for 30 minutes.

A tape test similar to that described in ASTM D 3359-02 was carried outon each sample. According to ASTM D 3359-02, a cross cut tool was usedto prepare vertical and horizontal parallel cuts on the sample surfaceto make a cross hatch pattern. A pressure sensitive tape was thenapplied on the cross hatch pattern and pressure was applied to flattenthe tape by using rubber erased on the back of a pencil.

The tape was then peeled off after waiting for 90 seconds by pulling itoff rapidly back over itself as close to an angle of 180°. The filmsurface was then inspected by microscope to see if any portion of thecoating was peeled off in the test. If some portion of the coating isremoved by the tape, the sample ‘fails’ the test. If no portion of thescored coating is removed, the sample ‘passes’. The samples including5%, and 10% Cymel 327 with respect to PMMA passed the tape test with nopeeling of the coating demonstrating improvement in PMMA overcoatadhesion when 5-10% Cymel 327 was added in the formulation.

Example 11 Reflowable Thick Overcoat with Good Contact Resistance andImproved Scratch Resistance

A transparent conductive layer with a thermoplastic overcoat wasprepared as follows. An ink was prepared containing 0.1 wt % silvernanowires, 0.2% HPMC (Methocel K100), and 250 ppm surfactant (Triton×100). The ink was coated onto eight, 4″×4″ single side hardcoat PETsubstrate (substrates were taped to 5″×5″ soda lime glass for spincoating using polyimide tape, ink coating was on the non-hard coatedside) by spin coating at 750 rpm for 60 seconds. The film was then driedat 50 degrees C. for 90 seconds, and baked at 140 degrees C. for 90seconds, resulting in a coating with a sheet resistance of approximately150 ohms/square.

Dianal MB 2752 (MW=17,000 gm/mol), available from Dianal America, Inc.was dissolved in PGMEA at a concentration of 15 wt %. Desmodur BL 3575(blocked isocynates crosslinker) was used as supplied (75 wt %).Desmodur BL 3575 was added quantitatively to Dianal MB 2752 solution toachieve solutions containing 30%, and 37.5% Desmodur BL 3575 relative tothe Dianal MB 2752.

Each Dianal MB 2752/Desmodur BL 3575 solution in PGMEA was spin coatedat 500 rpm for 60 seconds onto four separate 4″×4″ single side hardcoatPET substrate previously coated with nanowire layers as described inExample 10 to produce overcoats of approximately 1.5 μm thickness. Thesamples were dried at 50 degrees C. for 90 seconds, and baked at 100degrees C. for up to 10 minutes. One sample from each Dianal MB2752/Desmodur BL 3575 formulation was used for printing silver pastecontact for measuring qualitative contact resistance immediately afterpreparing.

Qualitative contact resistance was measured by screen printing rectanglepatterns on a 4″×4″ film prepared by the method mentioned above. Thepattern contains pairs of 4 mm×8 mm, 2 mm×4 mm, 1 mm×2 mm, and 0.5 mm×1mm contacts and the pattern is designed so that when contact resistanceis 0, total resistance between 4×8 mm contacts is the same as between2×4 mm contacts, and so on. So if a total resistance is higher for 1×2mm contacts than for 4×8 mm contacts, the difference is caused bycontact resistance. Toyobo DW-117-41T05 silver paste was used forprinting the contacts using Affiliated Manufacturers Inc. (ami) MSP-485screen printer installed with a rubber squeeze of 70 durometer hardness.A stainless steel screen with 250 mesh size was used for printing. Afterprinting, the samples (including the silver paste and the Dianal MB2752/Desmodur BL 3575 coatings) were cured at 130 degree C. for 30minutes. The total resistance measurements were done by using Keithleysystem source meter using 0.1 mA current and 10V compliance limit.Smallest contacts (0.5×1 mm) were measured using a multimeter.

The remaining three samples for each Dianal MB 2752/Desmodur 3575formulations were stored in individual 6″×6″ polypropylene clam shellcontainers in a cabinet. One sample from each formulation was removedafter storage time of 1.3 weeks (216 hrs), 7 weeks (1176 hrs) and 27.1weeks (4560 hrs) and subjected to qualitative contact measurementprocedure mentioned above. If the formulations are not stable, thenthere should be an increase in the total measured resistance indicatingthat the contact resistance of the top layer is increasing. The actualsheet resistances of the films were measured before screen printing tomake sure that there was no increase in the sheet resistance of thefilms because of the storage.

As shown in Tables 3 and 4 below, the qualitative contact resistancedata measured at 0, 1.3, 7 and 27.1 weeks for these films showed nosignificant differences in measure total resistance. Also totalresistance measured for different contact pad sizes did not show anysignificant increase form large to small contact pad sizes (data shownin the table below). This indicates that the films were relativelystable upon storage (little or no crosslinking reaction happened) andcould be cured after silver paste printing. The curing of the films wastested by wiping the film surface with a lab wipe wet with acetone andif the films were not cured properly then the coating could be easilywiped away. For all the films (stored at different times), the coatingdid not wipe away after wiping with acetone.

TABLE 3 Contact Dianal MB 2752 + 30% Desmodur BL 3575 Size T = 216 T =1176 T = 4560 (mm) T = 0 hrs hrs hrs 0.5 × 1   Average 77.1 70.6 69.972.6 Resistance (Ω) % Standard 8.3% 8.3% 8.5% 8.4% Deviation 1 × 2Average 67.3 66.0 70.7 70.0 Resistance (Ω) % Standard 7.5% 8.3% 9.4%8.4% Deviation 2 × 4 Average 63.6 66.0 65.7 67.7 Resistance (Ω) %Standard 6.2% 10.1% 9.5% 9.0% Deviation 4 × 8 Average 63.3 66.2 66.671.6 Resistance (Ω) % Standard 10.9% 9.1% 6.8% 20.6% Deviation

TABLE 4 Dianal MB Contact 2752 + 37.5% Desomodur BL 3575 Size T = 216 T= 1176 T = 4560 (mm) T = 0 hrs hrs hrs 0.5 × 1   Average 82.8 69.0 65.970.9 Resistance (Ω) % Standard 11.7% 7.8% 10.3% 10.5% Deviation 1 × 2Average 74.4 69.2 65.1 68.0 Resistance (Ω) % Standard 10.2% 7.4% 6.2%8.7% Deviation 2 × 4 Average 69.0 65.9 63.0 65.8 Resistance (Ω) %Standard 8.4% 5.9% 8.0% 6.3% Deviation 4 × 8 Average 68.2 65.6 66.6 67.2Resistance (Ω) % Standard 8.1% 9.0% 5.4% 7.2% Deviation

Example 12 Reflowable Thick Overcoat with Good Contact Resistance andImprove Scratch Resistance Using Powder Coating Resin

A transparent conductive layer with a thermoplastic overcoat wasprepared as follows. An ink was prepared containing 0.1 wt % silvernanowires, 0.2% HPMC (Methocel K100), and 250 ppm surfactant (Triton×100). The ink was coated onto two, 3″×3″ single side hardcoat PETsubstrate (substrates were taped to 4″×4″ soda lime glass for spincoating using polyimide tape, ink coating was on the non-hard coatedside) by spin coating at 750 rpm for 60 seconds. The film was then driedat 50 degrees C. for 90 seconds, and baked at 140 degrees C. for 90seconds, resulting in a coating with a sheet resistance of approximately150 ohms/square.

EPON 2002 (powder coating resin based on bisphenol A/epichlorohydrinepoxy resin), available from Momentive Specialty Chemicals Inc., wasdissolved in diacetone alcohol (DAA) at a concentration of 15 wt %.EPIKURE P 101 (Imidazole based curing agent for EPON 2002) was dissolvedat a concentration of 15 wt % in DAA. The two solutions were mixedtogether to achieve 5 wt % EPIKURE P 101 in the formulation relative toEPON 2002.

The EPON 2002/EPIKURE P 101 formulation was spin coated at 500 rpm for60 seconds onto two separate 3″×3″ single side hardcoat PET substratecoated with nanowire layers previously (as mentioned in the aboveparagraph) to produce overcoats of approximately 1.5 μm thickness. Thesamples were dried at 50 degrees C. for 90 seconds, baked at 100 degreesC. for up to 3 minutes to obtain a non-tacky film.

The samples were cut into a size of 46 mm×56 mm and screen printing wasused to print two silver bus bars (3 mm×44 mm) along the smaller edgefor resistance measurement. Toyobo DW-117-41T05 silver paste was usedfor printing the bus bars using Affiliated Manufacturers Inc. (ami)MSP-485 screen printer installed with a rubber squeeze of 70 durometerhardness. A stainless steel screen with 250 mesh size was used forprinting. After printing, the samples (including the EPON 2002/EPIKURE P101 coatings and silver paste) were cured at 130 degree C. for 30minutes. The total resistance of the film was measure using a multimeterand curing of the film was tested by wiping the coating with a wet labwipe soaked with acetone.

The total resistance measured for the two samples was 156.8 ohms and151.6 ohms and no overcoat wiping was observed after wiping with acetonesoaked lab wipe. This indicates that the uncured overcoat was stableduring the film processing (coating, drying, silver paste printing) andallowed for a very thick overcoat with very low contact resistance whichcan be further cured during the silver paste curing step to achievemechanically robust film.

The films prepared in Examples 11 and 12 were subjected to scratchresistance tests. The scratch resistance was measured using Elcometer3086 motorized Pencil hardness test. The hardness was assessed byfollowing ASTM method: ASTM D3363 according to a hardness scale fromsoft to hard: 2B, B, HB, F, H, 2H, 3H and 4H. The pencil hardness scalespans from B to 2H. The results are shown in Table 5.

TABLE 5 Overcoat type Overcoat Pencil (μm) Thickness (μm) Hardness 125μm single PMMA 2 HB-F side hard coat Dianal MB 2752 + 1.5 F-H PET coatedwith 30% Desmodur BL Silver nanowires 3575 Dianal MB 2752 + SubstrateH-2H 37.5% Desmodur BL 3575 EPON 2002 + 5% 5 wt 1.5 H-2H % EPIKURE P 101

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A method of forming a layered structure, the method comprising:providing a conductive layer on a substrate, the conductive layer havinga surface opposite from the substrate; forming one or more electricalcontacts on the surface of the conductive layer; forming an overcoatlayer over the one or more electrical contacts, the overcoat layercontacting the surface of the conductive layer uncovered by theelectrical contacts; and providing one or more via holes in the overcoatlayer, the one or more via holes extending through the overcoat layerand reaching at least some of the one or more electrical contacts. 2.The method of claim 1 wherein forming the overcoat layer comprisesdepositing and curing an overcoat material.
 3. The method of claim 2wherein the overcoat material is a reflowable polymer.
 4. The method ofclaim 3 wherein the reflowable polymer includes at least one materialselected from the group consisting of poly(methyl methacrylate), adissolved powder coating resin, a copolymer of methyl methacrylate, ahydroxyl functional monomer, a carboxylate functional monomer, an aminemonomer, and an epoxy monomer.
 5. The method of claim 2 wherein formingthe one or more via holes comprises laser ablating the overcoat layer atpredetermined locations.
 6. The method of claim 2 wherein forming theone or more via holes comprises dewetting the overcoat material at theone or more electrical contacts.
 7. The method of claim 1 whereinforming the overcoat layer comprising overlaying a functional film onthe surface of the conductive layer.
 8. The method of claim 7 whereinforming the one or more via holes comprises pre-cutting the functionalfilm at predetermined locations prior to overlaying the functional filmon the surface of the conductive layer.
 9. The method of claim 1 whereinforming the one or more electrical contacts comprises spot-depositing aformulation having conductive nanoparticles on the surface of theconductive layer.
 10. The method of claim 1 further comprising formingone or more electrical conduits through the one or more via holes,wherein the one or more electrical conduits contact the one or moreelectrical contacts.
 11. The method of claim 10 wherein the one or moreelectrical conduits are conductive wires, conductive adhesive or solder.12. The method of claim 1 wherein the conductive layer comprises aplurality of networking conductive nanostructures.
 13. The method ofclaim 12 wherein the conductive nanowires include silver nanowires,carbon nanotubes or a combination thereof.
 14. A layered structureformed by the method of claim
 1. 15. A layered structure comprising: asubstrate; a conductive layer formed on the substrate, the conductivelayer including a plurality of networking conductive nanostructures,wherein the conductive layer has a surface opposite from the substrate;one or more electrical contacts on the surface of the conductive layer;an overcoat layer overlying the conductive layer, wherein the overcoatlayer contacts the surface uncovered by the one or more electricalcontacts; and one or more via holes extending through the overcoat layerand reaching the one or more electrical contacts.
 16. The layeredstructure of claim 16 wherein the conductive nanostructures includesilver nanowires, carbon nanotubes or a combination thereof.
 17. Thelayered structure of claim 16 wherein each electrical contact includes aplurality of conductive particles.
 18. The layered structure of claim 16wherein the overcoat layer is a reflowable polymer or a functional film.19. The layered structure of claim 18 wherein the reflowable overcoat isa polymer or copolymer comprising acrylate monomers represented by thefollowing formula:

wherein, R¹ is hydrogen or alkyl, L is a direct bond, an alkylene chainor an alkylene oxide chain; R² is hydrogen, hydroxyl, amino (includingmono-, di-substituted amino), glycidyl, substituted or unsubstitutedalkyl, and substituted or unsubstituted aryl.
 20. The layered structureof claim 16 further comprising one or more electrical conduits extendinginto the one or more via holes and contacting the one or more electricalcontacts.